Fan Switch / Overheating

[A-V]

I bought my car with a broken fan switch. The fan was wired to be on all the time which I didn't know untill the wire burnt out and the car overheated.
I got a new fan switch installed and it was working but since being installed (2 weeks ago?) it failed today again. The engine was heating up quite high, the orange light was on and the fan wasn't. When I got home I heated up the car with the water cap off and put it on, but with the water going crazy the fan wasn't coming on. I've wired the fan to be on all the time, but I'm wary that the fan will eventually give up on me. Also, i've heard it can do the CAT in as well.
If the switch I bought was decent - Is this symptomatic of a more serious problem like a blown head gasket etc? Am I unlucky or is there something more sinister going on?

[dan-hipgrave]

well if its your headgasket then you will also have mayonnaise type stuff in your oil filler cap, and your coolant level will have dropped...

[ade]

I'd check the fan isnt knackered and your temp sensor/thermostat is working

I think this is right - When you first start the car, the engine gets hot then the theremostat will open a valve to allow coolant to circulate keeping it cool. When the coolant gets too hot (like youre standing still at traffic for ages) the temp sensor will turn the radiator fan on until the water cools (you can also turn your heating up full blast for a quick temp drop - which saved me overheating waiting to get into trax 2 yrs ago!)

I'd check the fuses & temp sensor

Ade

[A-V]

I was told that depending on whether the oil mixes with the water or v versa will determine whether u get mayonnaise or not.

If the gasket is ok, then have i been unlucky with the switch? or could something else be at fault?

[A-V]

How can i check the thermostat? - Thanks for the input lads

[Aragorn]

running the engine with cap off will cause the engine to boil over before fan kicks in

fan sensor operates at 100c and water wont reach 100c unless its a pressurised system - ie cap is on

stick a paperclip over the fan switch wires and make sure the fan spins up

if it does then get it fully warmed up by driving it for 10-15mins then stop and let it idle, temp should climb after 10-15mins and fan should kick in

it could be a semi-dodgy fan motor, give it a turn by hand and see if it feels really tight to rotate which could indicate dead bearings

[Dar]

To check your thermostat just take it off of the car and then boil the kettle. Pour some boiling water in to a cup and then place the thermostat in the water. It should then open. Its quite cool :mrgreen:

[A-V]

The fan defo works coz I've got it on all the time at the mo, ive linked the fan switch connectors together.

So to check the switch I should drive it 15 mins then after letting it run for a bit idle, the fan should come on?

I'll check out that thermostat trick, sounds quite neat.